Trigger problem

I have table anda data like this:

CREATE TABLE "aa" (
    "id"  serial,
    "d" bool DEFAULT 'f'::bool NOT NULL,
    "nid" int4
);

INSERT INTO "aa" ("id", "d", "nid") VALUES(1, 'f', 1);
INSERT INTO "aa" ("id", "d", "nid") VALUES(2, 'f', 1);
INSERT INTO "aa" ("id", "d", "nid") VALUES(3, 'f', 2);
INSERT INTO "aa" ("id", "d", "nid") VALUES(4, 't', 1);

My goal is:
when I update record id=2 and set d='t',
 I want to set all other records field d to 'f' where field nid contains the same
value as updated record.
In this situation I should set d to 'f' in record id=4


Any idea?


. Vladimir Manic, dipl. ing
. manix@eunet.yu
. manix@pakom.co.yu
. ICQ:23561543